Device for controlling a voltage-controlled power switch

ABSTRACT

A device for controlling a voltage-controlled switch, including two circuits respectively for setting to the high level and for setting to the low level a control terminal of the voltage-controlled switch, one at least of the circuits including a power transistor capable of connecting the control terminal to a high, respectively low voltage, a bipolar control transistor having its emitter, respectively its collector, connected to the control terminal of the power transistor, the base of the control transistor being likely to receive a control current and a first diode connected between a first predetermined voltage smaller than the high voltage, and the base of the control transistor.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to the control ofvoltage-controlled switches, and especially the control of powerswitches.

[0003] 2. Discussion of the Related Art

[0004] When a control voltage capable of making a voltage-controlledswitch operate in a desired conduction state is abruptly applied to saidswitch, an overcurrent tends to occur in the switch at the turning-on.In particular, in the case of a power switch connected to an inductiveload such as an electric motor winding capable of causing voltages onthe order of several tens of volts, the overcurrent is likely to damagethe switch. To avoid this problem, power switch control devices varyingthe voltage by stages have been provided. In the case where the powercircuit is for example a motor control circuit operating on the mains,and where the power switch is an IGBT or MOS power transistor, thecontrol circuit must provide high voltages and conduct high currents,and no control integrated device of such power switches is currentlyknown.

SUMMARY OF THE INVENTION

[0005] An object of the present invention is to provide an integratedand inexpensive device for controlling a voltage-controlled powerswitch.

[0006] To achieve this and other objects, the present invention providesa control device comprising a circuit for setting to the high stateand/or a circuit for setting to the low state.

[0007] More specifically, the present invention provides a device forcontrolling a voltage-controlled switch, comprising two circuitsrespectively for setting to the high level and for setting to the lowlevel a control terminal of the voltage-controlled switch; one at leastof said circuits comprising a power transistor capable of connecting thecontrol terminal to a high, respectively low voltage; a bipolar controltransistor having its emitter, respectively its collector, connected tothe control terminal of the power transistor, the base of the controltransistor being likely to receive a control current; a first diodehaving its cathode, respectively, its anode, connected to a firstpredetermined voltage smaller than the high voltage, and having itsanode, respectively its cathode, connected to the base of the controltransistor.

[0008] According to an embodiment of the present invention, said atleast one of said circuits is the circuit for setting to the high leveland it comprises a first output terminal capable of being connected tothe control terminal of the voltage-controlled switch; the power andcontrol transistors being first and second NPN-type bipolar transistorsforming a Darlington assembly arranged between the first output terminaland the high voltage; the anode of the first diode being connected tothe base of the control transistor via a first controllable circuitbreaker; and the device being capable of being connected to a controlblock successively enabling:

[0009] a/ applying the control current to the Darlington assembly andturning on the first circuit breaker; and

[0010] b/ after a first predetermined duration, turning off the firstcircuit breaker.

[0011] According to an embodiment of the present invention, the devicefurther comprises first and second P-channel MOS transistors havingtheir sources connected to the high voltage, a controllable currentsource being connected to the drain of the first MOS transistor, thegates of the first and second MOS transistors being connected to thedrain of the first MOS transistor and the drain of the second MOStransistor being connected to the base of the control transistor and tothe drain of a third N-channel MOS transistor, having its sourceconnected to a low supply voltage and the gate of which is capable ofbeing connected to the control block via a second controllable circuitbreaker, a second diode having its cathode and its anode respectivelyconnected to the drain of the third MOS transistor and to the firstoutput terminal.

[0012] According to an embodiment of the present invention, the firstcircuit breaker comprises a fourth P-channel MOS transistor having itssource connected to the base of the control transistor and having itsdrain connected to the anode of the first diode, the gate of the fourthMOS transistor being connected via a third resistor to the drain of afifth P-channel MOS transistor, the source of the fifth MOS transistorbeing connected to the high voltage, the gate of the fifth MOStransistor being connected to the gate of the first MOS transistor, thegate of the fourth MOS transistor being also connected: to the anode ofa first zener diode having its cathode connected to the anode of asecond zener diode having its cathode connected to the base of thecontrol transistor; to the anode of a third diode having its cathodeconnected to the base of the control transistor; and to the cathode of afourth diode having its anode connected to the drain of the fifth MOStransistor; a fifth diode having its anode connected to the drain of thefifth MOS transistor and its cathode connected to the drain of a sixthN-channel MOS transistor having its source connected to a ground voltageand the gate of which is capable of being connected to the controlblock.

[0013] According to an embodiment of the present invention, the secondcircuit breaker comprises a buffer circuit having an input terminal, anoutput terminal, and a control terminal, the output terminal of whichcan take three states: 1 or 0 according to whether the input terminal isat 1 or 0 when the control terminal is at 1, and a high-impedance stateif the control terminal is at 0.

[0014] According to an embodiment of the present invention, the device'scircuit for setting to the low level comprises a second output terminalcapable of being connected to the control terminal of thevoltage-controlled switch and comprising: a seventh N-channel MOStransistor arranged between the second output terminal and the lowvoltage, and the gate of which is capable of being connected to thecontrol block via the second controllable circuit breaker; and alimiting means controllable for, when the second circuit breaker is off,providing the gate of the seventh MOS transistor with an activationvoltage as long as the voltage of the second output terminal is greaterthan a predetermined voltage ranging between the high and groundvoltages; the control block enabling, upon activation of the Darlingtonassembly, provision of a deactivation signal to the gate of the seventhMOS transistor and, a second predetermined duration after theturning-off of the first circuit breaker:

[0015] c/ deactivation the Darlington assembly and turning off thesecond circuit breaker; and

[0016] d/ after a third predetermined duration, turning on the secondcircuit breaker and providing an activation signal to the gate of theseventh MOS transistor.

[0017] According to an embodiment of the present invention, the limitingmeans comprises a third bipolar transistor arranged between the secondoutput terminal and the gate of the seventh MOS transistor, and a sixthdiode capable of canceling the base current of the third bipolartransistor when the voltage of the second output terminal is smallerthan the second predetermined voltage.

[0018] According to an embodiment of the present invention, thecollector of the third bipolar transistor is connected via a fourthresistor to the gate of the seventh MOS s transistor, a fifth resistorconnecting the gate of the seventh MOS transistor to the low voltage,the base of the third bipolar transistor being connected to the cathodeof the sixth diode, having its anode connected to the secondpredetermined voltage, the base of the third bipolar transistor beingalso connected via a sixth resistor to the drain of an eighth N-type MOStransistor, having its source connected to the ground voltage and thegate of which is capable of being connected to the control block.

[0019] The present invention also aims at a control device in which saidat least one of said circuits is the circuit for setting to the lowlevel and comprises a first output terminal capable of being connectedto the control terminal of the voltage-controlled switch; the powertransistor being an N-channel MOS transistor and the control transistorbeing a PNP-type bipolar transistor having its emitter and its collectorrespectively connected to the drain and to the gate of the powertransistor, the gate of the power transistor being further connected tothe low voltage via a resistor and connected via a first controllablecircuit breaker to a control terminal of the power transistor; thedevice being capable of being connected to a control block enabling:

[0020] a/ deactivating the circuit for setting to the high level,turning off the first circuit breaker, and applying the control currentof the control transistor; and

[0021] b/ after a first predetermined duration, deactivating the controlcurrent of the control transistor, turning on the first circuit breaker,and providing an activation signal to the gate of the power transistor.

[0022] According to an embodiment of the present invention, the circuitfor setting to the high level comprises: a second output terminalcapable of being connected to the control terminal of thevoltage-controlled switch; a Darlington assembly arranged between thesecond output terminal and the high voltage, a control terminal of theDarlington assembly being likely to receive a control current; and asecond diode having its cathode connected to a second predeterminedvoltage smaller than the high voltage and its anode connected to thecontrol terminal of the Darlington assembly via a second controllablecircuit breaker; the control block enabling successively:

[0023] c/ providing a deactivation signal to the gate of the powertransistor, applying the control current of the Darlington assembly, andturning on the second circuit breaker; and

[0024] d/ after a second predetermined duration, turning off the secondcircuit breaker.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The foregoing objects, features, and advantages of the presentinvention will be discussed in detail in the following non-limitingdescription of specific embodiments in connection with the accompanyingdrawings.

[0026]FIG. 1 schematically shows an IGBT control device according to thepresent invention;

[0027]FIG. 2 illustrates the operation of the device of FIG. 1; and

[0028]FIG. 3 shows in detailed fashion an embodiment of controllablecircuit breakers of FIG. 1.

DETAILED DESCRIPTION

[0029] The same elements have been designated with the same referencenumerals in the different drawings. Only those elements necessary to theunderstanding of the present invention have been shown.

[0030] An embodiment of the present invention will be described in thecase where the voltage-controlled power switch is an insulated-gatebipolar transistor or IGBT. The present invention aims at a device forcontrolling a voltage-controlled switch, comprising two circuits (1, 17)respectively for setting to the high level and for setting to the lowlevel a control terminal of the voltage-controlled switch.

[0031]FIG. 1 schematically shows an embodiment of an IGBT control deviceaccording to the present invention, of which circuit 1 for setting tothe high level comprises a first output terminal OUTh capable of beingconnected to the gate of an IGBT not shown. Circuit 1 comprises a powertransistor 2 connected between a high supply voltage Vh and terminalOUTh and a control circuit for providing an activation signal totransistor 2. Circuit 1 also comprises a circuit activable to cancel theactivation signal of transistor 2 when the voltage of terminal OUThexceeds a voltage Von smaller than voltage Vh.

[0032] According to a feature of the present invention, power transistor2 is an NPN-type bipolar transistor and the control circuit oftransistor 2 comprises an NPN-type bipolar transistor 3. Transistors 2and 3 form a Darlington assembly: their collectors are connected tovoltage Vh and their emitters are preferably connected to terminal OUTh,each by a resistor. The base of NPN power transistor 3 is connected tothe emitter of NPN power transistor 2. The base of NPN controltransistor 3 forms the control terminal of the Darlington assembly.

[0033] The control circuit of transistor 2 further comprises twoP-channel MOS transistors 4 and 6 assembled as a current mirror, havingtheir sources connected to voltage Vh. The respective drains oftransistors 4 and 6 are connected to a current source 8 controllable inall or nothing and to the control terminal of the Darlington assembly.The respective sizes of transistors 4 and 6 are selected for transistor4 to consume a small current and for the current provided by transistor6 to enable fast activation of the Darlington assembly. The controlterminal of the Darlington assembly is also connected to the drain of anN-channel MOS transistor 10, having its source connected to a low supplyvoltage V1. The gate of transistor 10 is connected to a control terminal12 via a controllable circuit breaker 14. An embodiment of circuitbreaker 14 is described hereafter in relation with FIG. 3.

[0034] According to a feature of the present invention, the circuit forcanceling the activation signal of transistor 2 comprises a diode D1having its anode connected to the control terminal of the Darlingtonassembly via a controllable circuit breaker 16. The cathode of diode 151is connected to a predetermined voltage Von. An embodiment of circuitbreaker 16 is described hereafter in relation with FIG. 3.

[0035] Current source 8, control terminal 12, and circuits breakers 14and 16 are capable of being connected to a control block 30. Controlblock 30 may be integrated with the control device or on a separatechip, as shown by the dotted lines.

[0036]FIG. 2 illustrates the operation of circuit 1 for setting to thehigh level. Signals S8, S12, S14, and S16 respectively show the signalsprovided to elements 8, 12, 14, and 16. FIG. 2 also shows voltage Voutof terminal OUTh. It is considered that initially, current source 8 isdeactivated, that control terminal 12 is at a voltage capable ofactivating transistor 10, and that circuit breakers 14 and 16 arerespectively on and off (which is represented herein with signals S8,S12, S14, and S16 respectively at 0, 1, 1, 0). The activation oftransistor 10 maintains voltage Vout substantially at voltage V1.

[0037] At a time t0, block 30 activates current source 8, turns oncircuit breaker 16, and brings control terminal 12 to a voltage capableof deactivating transistor 10. Current source 8 conducts a current Is,whereby a current Im of fixed value is provided to the control terminalof the Darlington assembly. Current Im activates the Darlington assemblyand draws output terminal OUTh towards voltage Vh. The voltage of thecontrol terminal of the Darlington assembly is substantially equal tothe voltage of output terminal OUTh (the output voltage plus two diodethreshold voltages).

[0038] At a time t0+δt, corresponding to the time when the voltage ofthe control terminal of the Darlington assembly exceeds a value equal tovoltage Von plus the threshold voltage of diode D1, diode D1 turns on.For simplicity, it is considered hereafter that time t0+δt correspondsto a time when the voltage of terminal OUTh is substantially equal tovoltage Von. Diode D1 is selected so that its turning-on diverts fromthe control terminal of the Darlington assembly a portion of current Imsufficient to deactivate the Darlington assembly. The capacitor formedby the IGBT gate then remains substantially at voltage Von. In practice,transistors 4 and 6 and the Darlington assembly are selected for voltageVout to increase fast, and times to and t0+δt are very close.

[0039] At a time t1, a predetermined duration after time t0, block 30turns off circuit breaker 16. Current Im, which can then no longer runthrough diode D1, activates back the Darlington assembly which bringsterminal OUTh to a voltage substantially equal to voltage Vh. The IGBTis then completely activated.

[0040] The control device according to the present invention thusenables providing an increasing voltage Vout between V1 and Vh, with astage at a predetermined voltage Von for a controllable duration t1-t0.

[0041] To activate the IGBT, voltage Vout must be decreased from voltageVh to voltage V1. It is for this purpose possible to control block 30 todeactivate current source 8 and activate transistor 10, but voltage Voutthen decreases without stopping at a stage.

[0042] The present invention also provides that the control device cancomprise a specific circuit 17 for setting to the low level to decreasevoltage Vout with a stop at a stage.

[0043] As shown in FIG. 1, an embodiment of circuit 17 for setting tothe low level comprises a second output terminal OUT1 capable of beingconnected to the IGBT gate. In practice, terminals OUTh and OUT1 may beconnected together directly to the IGBT gate, or be connected to theIGBT gate via a resistive bridge. Circuit 17 comprises a powertransistor 18 connected to voltage V1, and capable of decreasing thevoltage of terminal OUT1. According to the present invention, powertransistor 18 is controllable either by a circuit enabling decreasingthe voltage of terminal OUT1 from voltage Vh to a voltage Voff rangingbetween Vh and GND, or by control block 30 to decrease the voltage ofterminal OUT1 from voltage Voff to voltage V1.

[0044] According to a feature of the present invention, power transistor18 is an N-channel MOS transistor 18 having its drain connected tooutput terminal OUT1 and its source connected to voltage V1. The gate oftransistor 18 is connected to control terminal 12 via circuit breaker14.

[0045] According to a feature of the present invention, the circuitenabling bringing terminal OUT1 to voltage Voff comprises a PNP-typebipolar control transistor 20 having its emitter connected to outputterminal OUT1, and having its collector connected via a resistor 22 tothe gate of transistor 18. A resistor 24 connects the gate of transistor18 to voltage V1. The base of transistor 20 is connected to the cathodeof a diode D2 having its anode connected to predetermined voltage Voff.The base of transistor 20 is also connected via a resistor 26 to thedrain of an N-type MOS transistor 28, having its source connected to aground voltage GND. A protection diode 32 has its cathode and anoderespectively connected to the control terminal of the Darlingtonassembly and to terminal OUTh. The gate of transistor 28 is capable ofbeing connected to control block 30.

[0046]FIG. 2 illustrates the operation of circuit 17 for setting to thelow level by means of preceding signals S8, S12, S14, and S16 and of asignal S28 representing the signal provided by block 30 to the gate oftransistor 28. Transistor 28 is initially deactivated. It is consideredin FIG. 2 that terminals OUTh and OUT1 are connected together and thatthey are at the same voltage Vout.

[0047] At a time t2 when the IGBT is desired to be activated, block 30deactivates current source 8, turns off circuit breaker 14, andactivates transistor 28 by bringing signal S28 from 0 to 1. Thedeactivation of current source 8 switches off current Im and deactivatesthe Darlington assembly. A current then flows from terminal OUT1 toground GND through emitter/base junction transistor 20, then throughresistor 26 and through transistor 28. The base current of transistor 20activates transistor 20, and creates a collector current which raisesthe gate voltage of transistor 18. Transistor 20 and resistors 22, 24are chosen so that transistor 18 is then activated and draws outputterminal OUT1 towards voltage V1. The base voltage of transistor 20 isequal to the voltage of output terminal OUT1 minus the base-emittervoltage of transistor 20.

[0048] At a time t2+δt′, corresponding to the time when the base voltageof transistor 20 falls below a value equal to voltage Voff minusthreshold voltage Vs of diode D2, diode D2 turns on. The on state ofdiode D2 maintains the base of transistor 20 at voltage Voff-Vs whilethe voltage of terminal OUT1 keeps on decreasing. When the voltage ofterminal OUT1 minus the base-emitter voltage of transistor 20 is smallerthan voltage Voff-Vs, the base-emitter junction of transistor 20 blocksand transistor 20 is deactivated. The gate voltage of transistor 18drops, which deactivates transistor 18. For simplicity, it is consideredhereafter that time t2+δt′ corresponds to a time when the voltage ofterminal OUT1, substantially equal to voltage Voff, stops decreasing.The capacitor formed by the IGBT gate then substantially remains atvoltage Voff. In practice, transistors 18 and 20 and resistors 22, 24are selected for voltage Vout to decrease fast, and times t2 and t2+δt′are very close.

[0049] At a time t3, a predetermined time after time t2, block 30 turnson circuit breaker 14, deactivates transistor 28, and brings controlterminal 12 to a voltage capable of activating transistors 10 and 18.The activation of transistors 10 and 18 lowers voltage Vout to voltageV1.

[0050] The voltage of the output terminal of the device according to anembodiment of the present invention thus decreases between Vh and V1,with a stage at a predetermined voltage Voff for a controllable durationt2-t3.

[0051] The values of Von and Voff are set by the user, for example, bymeans of zener diodes, so that Von<Vh and Voff>GND, with Von-GND>Vt andVh-Voff>Vt, where Vt is the threshold voltage of the controlled IGBT,the IGBT source being grounded.

[0052] Advantageously, the gates of transistors 10 and 18 areinterconnected, whereby transistors 10 and 18 can be activated ordeactivated together by means of a single control signal.

[0053]FIG. 3 shows a device such as shown in FIG. 1 in which anembodiment of circuit breakers 14 and 16 has been shown in detail.

[0054] Circuit breaker 14 comprises a buffer circuit 14′, the outputterminal of which can take three states: 1 or 0 according to whether itsinput terminal is at 1 or 0 or if a control terminal receiving signalS14 is at 1 (off circuit breaker), and a high-impedance state if thecontrol terminal receiving signal S14 is at 0 (on circuit breaker).

[0055] Switch 16 comprises a P-channel MOS transistor 36 having itssource connected to the control terminal of the Darlington assembly andhaving its drain connected to the anode of diode D1. The gate oftransistor 36 is connected via a resistor 38 to the drain of a P-channelMOS transistor 40. The source of transistor 40 is connected to voltageVh. The gate of transistor 40 and is connected to the gate of transistor4, so that transistor 40 forms a current mirror with transistor 4. Thegate of transistor 36 is also connected to the anode of a zener diode 42having its cathode connected to the anode of a zener diode 44 having itscathode connected to the control terminal of the Darlington assembly.The gate of transistor 36 is further connected to the anode of a diode46 having its cathode connected to the control terminal of theDarlington assembly, and to the cathode of a diode 48 having its anodeconnected to the drain of transistor 40. A diode 50 has its anodeconnected to the drain of transistor 40 and its cathode connected to thedrain of an N-channel MOS transistor 52 having its source connected toground GND. The gate of transistor 52 is connected to block 30, forexample, to receive control signal S16 illustrated in FIG. 2.

[0056] When signal S16 is at 1, transistor 52 is activated and draws thedrain of transistor 40 substantially to ground. The gate voltage oftransistor 36 is drawn to ground (said gate being connected to the drainof transistor 40 via resistor 38 which conducts no current as long as nocurrent is conducted by zener diodes 42, 44). As seen previously, whenthe voltage of the output terminal increases, the source voltage oftransistor 36, equal to the output voltage plus two diode thresholdvoltages Vbe, also increases. When Vt−Vgs>0, where Vt and Vgs arerespectively the threshold voltage and the gate-source voltage oftransistor 36, transistor 36 is activated. Switch 16 is then on. Thegate voltage of transistor 36 is limited to Vh−2Vz, where Vz is thezener voltage of diodes 42 and 44. Voltage 2Vz is selected to protectthe gate of transistor 36 while guaranteeing a low resistance Ron oftransistor 36. It should be noted that the device will operate even ifthe source-gate voltage of transistor 36 does not reach 2Vz.

[0057] When signal S16 is at 0, transistor 52 is inactive, the currentconducted by transistor 40 is provided to the control terminal of theDarlington assembly via diodes 48 and 46, the gate of transistor 36 isat a higher voltage than its source, and transistor 36 is deactivated.Circuit breaker 16 is then off. The size of transistor 40 is selected toprovide a current capable of rapidly charging the gate of transistor 36when signal S16 switches from 1 to 0, and this rapidly turns off circuitbreaker 16, with a reasonable power consumption. Diode 48 enablesgetting rid of the time constant which would otherwise be introduced byresistor 38.

[0058] Diode 50 blocks the way of the current when the voltage ofterminal OUTh becomes negative (when voltage V1 is negative). In theabsence of this diode, a current would then flow via the intrinsic diode(not shown) located between the source and the drain of transistor 52,and diodes 48 and 46, and would supply the Darlington assembly inundesirable fashion.

[0059] Of course, the present invention is likely to have variousalterations, modifications, and improvements which will readily occur tothose skilled in the art. In particular, the control device according tothe present invention has been shown as comprising both a circuit forsetting to the high level and a circuit for setting to the low levelaccording to the present invention, respectively enabling introductionof a stage at the rise and at the fall of the control voltage, but thoseskilled in the art will easily adapt the present invention to a controldevice only comprising a circuit for setting to the high level or acircuit for setting to the low level according to the present invention,for example, to introduce a stage at the rise only or at the fall onlyof the control voltage.

[0060] The present invention has been described in relation with thecontrol of an IGBT, but it will easily apply to the control of any othervoltage-controlled switch, for example, a MOSfet power transistor.

[0061] The present invention has been described in relation with adevice providing a voltage control signal stopping as it is rising at avoltage stage Von and as it is falling at a voltage stage Voff but thoseskilled in the art will easily adapt the present invention to a deviceproviding a voltage control signal stopping at a plurality of stages asit is rising and/or as it is falling, for example, by providing voltagesVon and/or Voff that can take a plurality of values.

[0062] The present invention has been described in relation with astructure comprising specific elements, but those skilled in the artwill easily replace the described elements with equivalent elements. Asan example, the described MOS transistors may be of DMOS or VDMOS type.Similarly, resistor 26 may be made of polysilicon or in the form of aso-called “diffused P” resistor, the substrate of which will be leftfloating. The Darlington assembly may comprise, as shown, transistorshaving their emitters connected to the output terminal via resistors, orcomprise transistors having their emitters directly connected to theoutput terminal. The three-state buffer circuit may also be replacedwith a three-state inverter circuit receiving an inverted controlsignal. Further, the two transistors of the Darlington assembly may beconfounded in a single bipolar transistor.

[0063] Such alterations, modifications, and improvements are intended tobe part of this disclosure, and are intended to be within the spirit andthe scope of the present invention. Accordingly, the foregoingdescription is by way of example only and is not intended to belimiting. The present invention is limited only as defined in thefollowing claims and the equivalents thereto.

What is claimed is:
 1. A device for controlling a voltage-controlledswitch, comprising two circuits respectively for setting to a high leveland for setting to a low level a control terminal of thevoltage-controlled switch; wherein one at least of said circuitscomprises: a power transistor capable of connecting the control terminalto a high, respectively low, voltage; a bipolar control transistorhaving its emitter, respectively its collector, connected to the controlterminal of the power transistor, the base of the control transistorbeing adapted to receive a control current; and a first diode having acathode, respectively an anode, connected to a first predeterminedvoltage smaller than the high voltage, and having its anode,respectively its cathode, connected to the base of the controltransistor.
 2. The control device of claim 1, wherein said at least oneof said circuits is the circuit for setting to the high level andcomprises a first output terminal capable of being connected to thecontrol terminal of the voltage-controlled switch; the power and controltransistors being first and second NPN-type bipolar transistors forminga Darlington assembly arranged between the first output terminal and thehigh voltage; the anode of the first diode being connected to the baseof the control transistor via a first controllable circuit breaker; andthe device being capable of being connected to a control blocksuccessively enabling: a/ applying the control current to the Darlingtonassembly and turning on the first circuit breaker; and b/ after a firstpredetermined duration, turning off the first circuit breaker.
 3. Thecontrol device of claim 2, wherein the device further comprises firstand second P-channel MOS transistors having sources connected to thehigh voltage, a controllable current source being connected to the drainof the first MOS transistor, the gates of the first and second MOStransistors being connected to the drain of the first MOS transistor andthe drain of the second MOS transistor being connected to the base ofthe control transistor and to the drain of a third N-channel MOStransistor, having its source connected to a low supply voltage and thegate of which is capable of being connected to the control block via asecond controllable circuit breaker, a second diode having its cathodeand its anode respectively connected to the drain of the third MOStransistor and to the first output terminal.
 4. The control device ofclaim 3, wherein the first circuit breaker comprises a fourth P-channelMOS transistor having its source connected to the base of the controltransistor and having its drain connected to the anode of the firstdiode, the gate of the fourth MOS transistor being connected via a thirdresistor to the drain of a fifth P-channel MOS transistor, the source ofthe fifth MOS transistor being connected to the high voltage, the gateof the fifth MOS transistor being connected to the gate of the first MOStransistor, the gate of the fourth MOS transistor being also connected:to the anode of a first zener diode having its cathode connected to theanode of a second zener diode having its cathode connected to the baseof the control transistor; to the anode of a third diode having itscathode connected to the base of the control transistor; and to thecathode of a fourth diode having its anode connected to the drain of thefifth MOS transistor; a fifth diode having its anode connected to thedrain of the fifth MOS transistor and its cathode connected to the drainof a sixth N-channel MOS transistor having its source connected to aground voltage and the gate of which is capable of being connected tothe control block.
 5. The control device of claim 3, wherein the secondcircuit breaker comprises a buffer circuit having an input terminal, anoutput terminal, and a control terminal, the output terminal of whichcan take three states: I or 0 according to whether the input terminal isat 1 or 0 when the control terminal is at 1, and a high-impedance stateif the control terminal is at
 0. 6. The control device of claim 2,wherein the circuit for setting to the low level comprises a secondoutput terminal capable of being connected to the control terminal ofthe voltage-controlled switch and comprising: a seventh N-channel MOStransistor arranged between the second output terminal and the lowvoltage, and the gate of which is capable of being connected to thecontrol block via the second controllable circuit breaker; and alimiting means controllable for, when the second circuit breaker is off,providing the gate of the seventh MOS transistor with an activationvoltage as long as the voltage of the second output terminal is greaterthan a predetermined voltage ranging between the high and groundvoltages; the control block enabling, upon activation of the Darlingtonassembly, provision of a deactivation signal to the gate of the seventhMOS transistor and, a second predetermined duration after theturning-off of the first circuit breaker: c/ deactivating the Darlingtonassembly and turning off the second circuit breaker; and d/ after athird predetermined duration, turning on the second circuit breaker andproviding an activation signal to the gate of the seventh MOStransistor.
 7. The control device of claim 6, wherein the limiting meanscomprises a third bipolar transistor arranged between the second outputterminal and the gate of the seventh MOS transistor, and a sixth diodecapable of canceling the base current of the third bipolar transistorwhen the voltage of the second output terminal is smaller than thesecond predetermined voltage.
 8. The control device of claim 7, whereinthe collector of the third bipolar transistor is connected via a fourthresistor to the gate of the seventh MOS transistor, a fifth resistorconnecting the gate of the seventh MOS transistor to the low voltage,the base of the third bipolar transistor being connected to the cathodeof the sixth diode, having its anode connected to the secondpredetermined voltage, the base of the third bipolar transistor beingalso connected via a sixth resistor to the drain of an eighth N-type MOStransistor, having its source connected to the ground voltage and thegate of which is capable of being connected to the control block.
 9. Thecontrol device of claim 1, wherein said at least one of said circuits isthe circuit for setting to the low level and comprises a first outputterminal capable of being connected to the control terminal of thevoltage-controlled switch; the power transistor being an N-channel MOStransistor; and the control transistor being a PNP-type bipolartransistor having its emitter and its collector respectively connectedto the drain and to the gate of the power transistor, the gate of thepower transistor being further connected to the low voltage via aresistor and connected via a first controllable circuit breaker to acontrol terminal of the power transistor; the device being capable ofbeing connected to a control block enabling: a/ turning off the firstcircuit breaker, and applying the control current of the controltransistor; and b/ after a first predetermined duration, deactivatingthe control current of the control transistor, turning on the firstcircuit breaker, and providing an activation signal to the gate of thepower transistor.
 10. The control device of claim 9, wherein the circuitfor setting to the high level comprises: a second output terminalcapable of being connected to the control terminal of thevoltage-controlled switch; a Darlington assembly arranged between thesecond output terminal and the high voltage, a control terminal of theDarlington assembly being likely to receive a control current; and asecond diode having its cathode connected to a second predeterminedvoltage smaller than the high voltage and its anode connected to thecontrol terminal of the Darlington assembly via a second controllablecircuit breaker; the control block enabling successively: c/ providing adeactivation signal to the gate of the power transistor, applying thecontrol current of the Darlington assembly, and turning on the secondcircuit breaker; and d/ after a second predetermined duration, turningoff the second circuit breaker.